The article discusses global cities - the economic, political and financial centres of the modern world. However, the author does not focus on the economic importance of global cities but on their socio-cultural uniqueness. In this perspective cities are perceived as the most advanced evolutionary form of urban organisms, which developed during post-industrial globalisation. The latter made modern global cities centres with free movement of people and migrations as their inalienable features. By reference to Ulf Hannerz' concept of transnational connections the author discusses four main social categories that make up global cities: representatives of international business, populations originating in the Third World, the people of culture and tourists. While describing all four of them, the author draws attention to the consequences that the presence of these groups have in the cultural, social and spatial dimensions.